How can I decrypt an encrypted MCRYPT_RIJNDAEL_256 value in C#, that was encrypted by mcrypt in PHP?

Question

I am trying to read a Base64-Encoded value from a Database table managed on the Linux side. In that table there is a column called first_name. On the Linux side I can decrypt t

Answer 1

I hit the same problem when comunicating with a legacy system. I had to come up with my own solution as Rijndael with a Blocksize of 256 seems to be not supported by dotnet core.

Here is my solution using the bouncy castle library:

    public static byte[] Rijandael256Decrypt(byte[] inputBytes, byte[] keyBytes)
    {
        // set up
        IBufferedCipher cipher = new PaddedBufferedBlockCipher(new RijndaelEngine(256), new ZeroBytePadding());
        KeyParameter keyParam = new KeyParameter(keyBytes);
        cipher.Init(false, keyParam);
        int sizeAtLeastRequired = cipher.GetOutputSize(inputBytes.Length);
        byte[] outputBytes = new byte[sizeAtLeastRequired];

        // decrypt            
        int length = cipher.ProcessBytes(inputBytes, outputBytes, 0);
        length += cipher.DoFinal(outputBytes, length);

        // resize output
        Array.Resize(ref outputBytes, length);
        return outputBytes;
    }